The battle at lake Regillus

Intro
The battle at lake Regillus was a battle of Rome against a number of latin cities. There had been a peace treaty but since the fall of Tarquinius Superbus , they regarded this treaty as no longer valid. The former king had incited these cities to do so and liberate themselves from Rome. Of course he was still trying to regain his throne.

T. Livius
It is not clear when the battle at lake Regillus took place, not even in which year. According to T.Livius it all happened in the year 499 bc, the year of the consuls T. Aebutius Helva and P. Veturius Geminus Cicurinus. Also they would have appointed dictator: T. Aebutius Helva who appointed P. Veturius as his magister equitum (see Livius 2.19-20 )

Dionysius of Halicarnassus
Dionysius of Halicarnassus tells us that the battle at lake Regillus was in the year 496 bc. A. Postimius Albus and T. Tricostus Caeliomontanus were the consuls of that year Postimius was appointed dictator and he choose T. Aebutius Helva as his master of the horse.

Forces
As always Livius doesn't bother to give many details where Dionysius offers more. He even puts a speech of three chapters in the dictator's mouth. The Romans were to have 23700 foot and 1000 horse against 40000 foot and 3000 horse at the side of the Latins. These figures are probably exaggerated since this would mean Rome had far over 50,000 inhabitants at that time.

Castor and Pollux
This battle was won by the Romans, maybe because (according to Livius 2.20) the dictator had vowed a temple for Castor and Pollux , as Livius tells us or probably because the Romans were better trained and had better commanders. Dionysius(6.13) goes even a step further:

Divine help
"The next day, when those at the head of affairs received the letters from the dictator, and besides the other particulars of the battle, learned also of the appearance of the divinities, they concluded, as we may reasonably infer, that it was the same gods who had appeared in both places, and were convinced that the apparitions had been those of Castor and Pollux. Of this extraordinary and wonderful appearance of these gods there are many monuments at Rome, not only the temple of Castor and Pollux which the city erected in the Forum."

Phalanx
It is remarkable to see that Livius speaks of maniples and cohorts two types of army units yet to be invented, very likely the Romans and the Latins as well used the phalanx. From the description of Dionysius one could conclude there was no phalanx after the battle had started: officers fighting enemy officers when they see one. It is clear we don't know a lot of this battle. It is also very possible the whole battle is mythical.